Best version of each FF game? Up to FFX lets say.
FF1/2/3/4 PSP (even though 1/2 are easy as fuck, the art makes up for it)
FF9 PSX (PC port will be shit lets be honest)
PS1 version for FF1 and 2. They fix a lot of glitches while maintaining some of its mechanics like the Vatican spell system in Final Fantasy I and the stat growth along with degradation in Final Fantasy II.
I don't know if you're talking about the remake or the port, but the former isn't out yet and the latter looks like hot garbage. Either PSX or PC under specific circumstances is best.